In the inventor's prior Chinese patent ZL00123491.9, a liquid cold/hot source system by using water of river, lake or sea as an energy source was disclosed. The system is such a liquid cold/hot source system, which uses water of river, lake or sea as energy source, is free of pollution, occupies relatively small area, and can supply domestic hot water. However, a heat collecting device of this system should be positioned below the fluid surface of river, lake or sea. Since water of river, lake or sea keeps flowing and often arises large or even drastic fluctuation, it is much inconvenient to install and maintain the heat collecting device. In addition, the heat collecting device can not operate normally due to the fluctuation of water of river, lake or sea, and especially in winter, the frozen water of river, lake or sea will directly influence the normal operation of the system.